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A destructive derecho — a rare, powerful, and long-reaching
windstorm that accompanies lines of thunderstorms — swept from
the Midwest to the East Coast on Friday, June 29, and a new video
stitched together from satellite images shows the storm's furious
progress.

To qualify as a derecho — the Spanish word for "straight," and
pronounced deh-REY-cho — a storm must pack wind gusts of at least
58 mph (93 kph) throughout, and must cause wind damage across an
area at least 240 miles (400 kilometers) wide.

Although the full power of the recent storm is still emerging, it
appears it exceeded the qualifying requirements.
The derecho moved approximately 450 miles (724 km) in six
hours, at an average speed of 75 mph (120 kph). It swept
southeast from northwestern Indiana, across Ohio, and into
Pennsylvania and West Virginia, according to preliminary numbers
from the National Oceanic and Atmospheric Administration's Storm
Prediction Center.

Damage surveys uncovered wind speeds of 100 mph (160 kph) in
Zanesville, Ohio, and Preston County, W. Va., said Fred McMullen,
a meteorologist with the National Weather Service office in
Pittsburgh. "That's the same as
a Category 2 hurricane," McMullen told OurAmazingPlanet.

The storm downed power lines, and toppled trees from Illinois to
Washington, D.C. Wide regions of the Mid-Atlantic states are
still without power.

Derechos are extremely difficult to predict, but forecasters
aren't expecting a repeat of Friday's weather any time soon.
McMullen said they happen in his area about once a decade, and
are fueled by the same conditions that give rise to thunderstorms
— essentially, when cool air runs into hot air.

"We expect showers and thunderstorms today, but we don't think
we're going to get a huge wind event like we had on Friday," said
Brian Lasorsa, a meteorologist with the National Weather
Service's Baltimore/Washington, D.C., office. "There is a
potential for damaging wind gusts, but it's not as widespread."

McMullen said that aside from thunderstorms that could hit today
and during the Fourth of July holiday, the main concern is the
heat forecastthrough the end of the week. In the Mid-Atlantic
states, highs are expected to hover in the mid to low 90s, and
many people may not have electricity until the weekend.